The present invention relates to a polycrystalline abrasive material.
Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. They generally contain ultra-hard abrasive particles dispersed in a second phase matrix or binder phase. The matrix or binder may be metallic or ceramic or a cermet. It may be continuous in three dimensions. The ultra-hard abrasive particles may be diamond, cubic boron nitride (cBN), silicon carbide or silicon nitride and the like. These particles may be bonded to each other during the high pressure and high temperature compact manufacturing process generally used, forming a polycrystalline mass, or may be bonded via the matrix of second phase material(s) to form a polycrystalline mass. Such bodies are generally known as polycrystalline diamond or polycrystalline cubic boron nitride, where they contain diamond or cBN as the ultra-hard abrasive, respectively.
Examples of diamond and cubic boron nitride abrasive compacts are described in U.S. Pat. Nos. 3,745,623; 3,767,371; 3,743,489; 4,334,928; 5,466,642 and 5,328,875.
Conventional sintered bodies will typically have a bonding phase with a thickness or mean free path that varies considerably throughout the bulk of the material. That is, there are regions which contain larger amounts of binding phase and regions which contain lesser amounts. This is typically characterized as lacking the property of homogeneity by those skilled in the art. This lack of consistency of material structure has obvious effects on the overall performance of the material in application.
European patent EP 0 974 566 B1 describes the use of metallurgical, scanning, transmission, and Auger electron microscopy to measure the thickness of the bonding phase in a cBN (cubic boron nitride) sintered body comprising cBN particles and a bonding phase that bonds the cBN particles. Direct measurement of the thickness of the bonding phase, by drawing an arbitrary straight line on the micrographs, and image analysis were used to determine the average and standard deviation values of the thickness of the bonding phase for a range of sintered materials.
In EP 0 974 566 B1, the standard deviation of the thickness of the bonding phase is employed as a metric for evaluating the effectiveness of different material mixing methods. The lower the standard deviation, the more effective the mixing method was in homogeneously distributing the bonding phase.
By enhancing the homogeneity of the polycrystalline compact of the present invention (i.e. the relative distributions of ultrahard abrasive particles and matrix or binder material) through optimising the method or route of manufacture, a material of improved properties can be achieved.